1. Field of the Invention
The invention relates generally to high-precision servomechanisms, and more particularly to selfsynchronizing motors in servomechanisms.
2. Discussion of Background
These servomechanisms often use a selfsynchronizing motor without brushes which requires the use of an inductive sensor for the determination of the position of the rotor. Moreover, the use of the servomechanism requires a tachometer to determine at any moment the exact rotation speed of the rotor. Therefore, it is tempting to try to avoid the duplication of equipment and to determine the speed directly from the resolver. Generally the problem therefore occurs of generating a tachometry signal from an inductive sensor such as a resolver (biphase), a synchro (triphase) or an Inductosyn (linear displacement).
To solve this problem a device is already known, described in particular in European application No. 127 890. This prior device uses an RC circuit driven by the two signals of phases of the inductive sensor, itself fed by a sinusoidal reference signal. This RC circuit generates a sinusoidal analog signal whose phase angle is rigorously equal to the angular shift of the rotor of the sensor in relation to the stator. This analog signal then is digitized by a trigger circuit or the like to supply a square-wave input signal. Further, the oscillator which supplies said reference signal is made also to supply a second reference signal out of phase by .pi./2, these two reference signals also being digitized.
Moreover, this device uses two digital phase comparators consisting essentially of two exclusive OR gates respectively comparing said input signal and one of the two reference signals to generate two square-wave width modulation signals with alternately increasing and decreasing widths. These signals are separately filtered and shunted to generate a trapezoidal signal as well as this same signal out of phase by .pi./2, these two latter signals themselves being separately processed by inverters to obtain finally four trapezoidal signals out of phase by .pi./2 whose amplitudes are proportional to the speed of rotation. Finally the device comprises a complex logic which, starting from the two filtered signals, samples from each of the four preceding trapezoidal signals the two central quarters of each half period.
However, if a correct tachometry signal is desired, it is necessary to pair the components of the two ways. In adjustment to zero of the two shunting devices and also an adjustment to zero of the two inverters is also necessary, as otherwise there would be obtained, for example, for a constant rotation speed of nonconstant tachometry, a signal over a rotation.